SARS: Beyond Amoy Gardens

By Amesh A. Adalja, FACP, FACEP, December 20, 2013

The 2003 outbreak of SARS coronavirus that occurred in Hong Kong's 19-building Amoy Gardens housing complex is perhaps the most striking example of just how easily this virus can spread. The outbreak followed airborne transmission of virus from a visitor to the complex who had diarrhea and used a toilet. The resulting 331 cases represent the largest community outbreak of SARS.

On the 10th anniversary of the SARS outbreak, a research team from the Chinese University of Hong Kong revisited the Amoy Gardens outbreak to assess whether the airborne spread of SARS extended beyond the housing complex. Their study results, recently published in Clinical Infectious Diseases, indicate that the virus did spread further than originally recognized.

Evidence of Airborne Spread to Other Buildings

Using data on all SARS cases that occurred in Hong Kong, the research team divided cases into 3 groups based on geographic location: residents of Amoy Gardens (331 cases), residents of neighboring buildings (103 cases), and residents of other locations in the district. Epidemic curves were derived for each group, with a focus on cases occurring 5-10 days after the initial case patient visited Amoy Gardens.

The epidemic peak for Amoy Gardens occurred on March 24-25, 2003, and on March 25 for cases in neighboring buildings. There was no discernable peak for cases in other locations.

Most of the Amoy Gardens cases occurred in the A-G section of the complex, downwind from which was an adjacent building where 48 cases occurred. Similar but smaller clusters of cases in other nearby buildings with direct paths to Amoy Gardens were also described. Maps included in the article indicate that buildings to the north, west, and south of the housing complex experienced cases.

Containment Strategies May Need Revision

There is no vaccine or antiviral for SARS. If a new outbreak should occur, the findings of this study will have significant implications for public health interventions. It has been acknowledged that the Amoy Gardens complex had some unusual plumbing features that may have contributed to aerosolization of contaminated waste material; nonetheless, it is surprising that infectious doses of virus-laden aerosol were able to spread so far. If SARS and other viruses can be transmitted via airborne particles spread more than 200 meters, then containment will be very difficult, if not impossible. Isolation of suspected and confirmed cases in a residential building may not guarantee the virus will be kept at bay, which is what many public health preparedness plans for SARS rely on—self-isolation at home. Clearly, the results of this study should prompt reconsideration of those plans and renewed commitment to development of countermeasures.